What this does is instead of IIS starting by sending the page as a webpage it sends it as a word document. Don't ask me to explain, I don't know the exact details but the browser gets a message saying "This ain't ur standard webpage our kid...this is a word document" and your browser thinks "ooooh...now in this ere list if it's a word document I gotta open word to show this...". If you don't get word then it's either not installed or your browser's not configured to open word when it sees "application/msword"